Method and apparatus for etching metal by immersion



E. L. BREVIK 3,320,105

METHOD AND APPARATUS FOR ETCHING METAL BY IMMERSION May 16, 1967 Filed June 5, 1964 ELMER LAWRENCE BREVIK United States Patent 3,320,105 I'VIETHOD AND APPARATUS FOR ETCHING METAL BY IMMERSION Elmer Lawrence Brevik, Los Angeles, Calif., assignor to Chemical Milling International Corporation, El Segundo, Calif a corporation of California Filed June 3, 1964, Ser. No. 372,740 5 Claims. (Cl. 156-2) This invention pertains to a tank and associated equipment for etching of metal objects in a liquid medium or for the treating of objects in a liquid medium other than etching and in which a liquid is employed having a very low vapor pressure or a noxious odor.

In the past it has been the practice to employ open tanks for the purpose of etching metal objects in acid or alkaline solutions, depending upon the characteristics of the metal. The fumes developed from the etching of the metal, consisting of particulate matter carried out of the tank as a liquid envelop of etching solution surrounding hydrogen gas or the vapors of the etching solution consisting of the gases dissolved in water such as nitric or hydrochloric acid fumes, are generally very noxious and produce harmful eflects upon animal or plant life in the vicinity and in many instances cause harmful corrosive effects upon structures and equipment. To overcome these objectionable features of open tank etching solutions, fume collectors have been employed. Generally these consist of fume ducts arranged on two or more sides of the treating tanks; these ducts are then connected to a fume scrubber which employs either water or some other liquid through. which the fumes are passed or intimately dispersed which absorb the fumes and which water or other fluid is subsequently disposed of or treated to recover the collected products. The fumes are forced into the fume ducts and subsequently into the scrubber by reduced pressure created by a fan-type blower apparatus or a venturi which is so constructed as to create a reduced pressure area along the fume ducts.

The numerous disadvantages of this type of construction are apparent; with this type of equipment for handling corrosive fumes it is necessary to construct the entire fume system of costly corrosive resistant materials. In the static parts of the apparatus, plastics can quite frequently be utilized in construction and, though costly, they are generally cheaper than the corrosive resistant metals which would be required. In the moving part of the apparatus such as the blower or venturi however, it is almost mandatory that metals be used, particularly for shafts, bearings and rotors; frequently the cost of this part of the apparatus becomes prohibitive and it has been necessary to permit the fumes to escape into the atmosphere or abandon the project entirely.

Another disadvantage has been the low efliciency of the fume collectors. In general, the principle of collection of fumes from the sides of the tanks has been effective only on very narrow tanks as the power requirements and the air flow necessary for comparatively effective removal of the fumes varies roughly with the square of the Width of the tank so that, for example, a tank of four feet width would require four times the power of blower capacity of a tank of two-foot width. When the width of the tank exceeds ten feet, the efficient collection of fumes becomes practically impossible in an open tank and it becomes necessary to employ covers on the tank at all times in addition to the use of the fume collector system.

A further disadvantage of the presently employed apparatus is the increased loss of volatile ingredients in the liquid. It is very apparent that a high velocity stream of air passing over the surface of the fluid will increase the 3,32%,lfl5 Patented May 16, 1967 evaporation rate of the fluid and particularly the rate of loss of the volatile ingredients of the liquid.

A still further disadvantage of this type of apparatus is that the corrosive or noxious fumes must be collected in another fluid in the collector which is relatively dilute so that they are readily absorbed by the fluid in the collector. If the collector fluid approaches the concentration of the ingredients in the bath the efliciency of the collector becomes zero and the volatiles will be returned to the atmosphere as if the collector system were not employed. it is therefore apparent that the collector fluid must be treated continuously to remove the corrosive or noxious ingredients which it absorbs or it must be continuousiy diluted. In either instance, the removal from the collector requires additional recovery equipment. If water is used the corrosive water from the collector must be treated with a neutralizing agent before it is sewered or the sewage lines and equipment will be corroded. many areas, the amount of water available for industrial uses is becoming more and more critical so that water wasted in this manner is becoming more limited.

Although I have referred to the etching of metal as a typical example of the type of process carried out in this type of apparatus, there are numerous examples of other processes which employ this type of apparatus; to cite a few, solvent clegni{ig,1p lating, anodizing, chromadizing,

hatin an tie ike. ther mz thods, even less sophisticated than those described are still in use today; these consist of covers for the entire tank which must be removed each time entry is necessary; or the use of a non-miscible fluid of lower specific gravity than the active fluid so that the second fluid floats on the surface of the first and thereby prevents evaporation of the active fluid. system has the disadvantage of emulsification or mixing of the two fluids during movement of the objects to be treated which permits the lower layer of fluid to be exposed to the atmosphere and subsequent loss through evaporation. It is also apparent that it is impossible to have two fluids which are not, to a degree, mutually soluble in each other so that the floating fluid acts as a transmitter through which the lower layer of fluid will pass and thereby be lost to the atmosphere. l

In some instances, refrigeration or air cooling is employed around the top of the tank, as is the case of a conventional vapor degreaser; but the effective area of con densation is even more limited than in the case of the fume ducts, this type of apparatus is very ineflicient and ensive.

l t is therefore apparent that although the problemcf the elimination or removal of fumes from processing tanks has been known to exist for a long time, the methods used to date have been very ineffective in the SO lUHOD of the problem. It is, therefore, the object of my invention to provide a new and unique method for minimizing the amount of fumes that will be generated by a processing tank. It is the further object of my invention to remove any noxious fumes generated during the processing of objects in tanks without the use of expensive fume collection systems.

It is still a further object of my invention to prov de a fume collecting system for any sized tank, irrespective of its surface area.

It is still a further object of my invention to provide an apparatus which will use high vapor pressure developed by highly volatile fluids or the pressure generated by products formed during the processing as the motivation power for my collector system.

My invention consists of a processing tank so constructed that the entire area above the processing area in the tank is completely enclosed with a vapor-tight cover,

3 which vapor area is vented to the atmosphere through a very small fume collector or some other type of apparatus which will absorb the irritating or corrosive ingredients in the fumes.

Further objects and advantage of my invention will be more clearly understood by the following description and reference to the accompanying drawings in which:

FIGURE 1 is a perspective view of a modification of my invention showing a cut-away of the gas-tight area.

FIGURE 2 is a section view of the tank and vapor collecting apparatus through Section 22 of FIGURE 1.

In the drawing the numeral refers to a processing tank for containment of a fluid which tank consists of the tank proper, and vapor-tight partial cover 12 which terminates at a vertical member 13 which is likewise connected to the cover and the sides of the tank to produce a vaportight seal. The tank is filled with the processing liquid 14 to such a depth that vertical member 13 extends into the liquid to a non-critical depth such that a vapor-tight chamber 15 is formed bounded by tank'walls 11, cover 12, vertical member 13 and the liquid surface 14.

As volatile ingredients evaporate or pressure is built up in the enclosed area by the generation of hydrogen gas as in a metal etching operation, this pressure is relieved by passage through vent 18 and the gas passes into a scrubber 16 consisting of a body 17 which is partially filled with aggregate, raschig rings, saddles on the like as denoted by 21. The fumes are then removed from the vapor by the passages of an absorbing liquid such as water which is introduced into the scrubber through pipe 20 such that the absorbing liquid trickles over the aggregate which provides a large surface area for absorption purposes. The absorbed vapor and the absorbing fluid are then discharged through pipe 22 and are then sent to sewer or to recovery apparatus if they are of commercial value. Non-absorbed, non-noxious gases can then be vented to the atmosphere or to other recovery aparatus through vent 1?.

To clearly demonstrate one modification and purpose of any invention, particular reference is made to FIGURE 2 in which a bucket 24 of steel parts 23 are introduced into the etching chamber of the liquid by handle 25. If the liquid is a volatile acid such as nitric acid, the nitric acid attacks the steel producing such gaseous material as hydrogen and nitrogen oxides 26 which are not soluble in the liquid 14 and which tend to rise to the surface of the liquid and be trapped in the vapor-tight area 15. In rising to the surface the bubbles carry with them not only the hydrogen and relatively insoluble nitrogen oxides but also nitric acid and water vapor. As the gas is generated, the pressure is increased in the vapor-tight area so that, to equalize this pressure increase, the vapors are forced out 18 into the fume collector 16; Water is introduced into the collector through 20 in such. quantities that it absorbs the water soluble nitric acid, nitrogen oxides and water vapor. The hydrogen produced by the reaction is not readily absorbed by the water and is vented through exhaust 19 Where it is permitted to escape to the atmosphere, is burned or compressed.

It is apparent from this description that the gist of my invention consists of a reaction chamber covered with a vapor-tight cover which chamber is sealed 'by the liquid level of the processing liquid such that as pressure is created by the evaporation of volatile liquid or the generation of a relatively insoluble gas in the reaction area,

pressure is built up in the vapor-tight chamber which is used as the driving force for moving vapor-laden fumes into the scrubber.

It will be obvious to those skilled in the art that the invention as represented by the drawings and specifications will have several adaptable variations such as a tank in which work could be introduced in one end and removed on the other which would be an adaptation amenable to a conveyorized operation; or in place of the fume scrubber as shown the gases could go directly to a compressor for recovery.

It would also be apparent to those skilled in the art that the composition of the fluid is immaterial to the mechanism of operation of my invention. And further that, although no provision is made for the removal of fumes from the surface of the liquid exposed to the atmosphere, this area could be provided with conventional fume removal apparatus.

Therefore, it will be understood that which I claim as my invention is a new and novel apparatus for processing parts in a liquid medium in which fumes are generated either from the liquid itself or the processing operation and which through the practive of my invention eliminates the necessity for exterior power requirements for removal of vapor-laden fumes and generated gases.

I claim:

1. A process for treating a workpiece in a liquid media wherein the liquid is confined in a tank which is partially covered and which cover is sufficiently extensive to enclose the entire portion of the tank immediately above the workpiece by a vapor-tight seal between the tank and the cover on one or more sides, the remaining sides of the cover extending into the interface of the liquid, and exhausting the vapor confined under the cover through a collector by its own motive power.

2. The process of claim -1 wherein the workpiece is metal and the liquid is an etchant which reacts with the metal to produce hydrogen.

3. The process of claim 1 wherein the liquid is a volatile solvent.

4. Apparatus for containing a volatile liquid consisting of a tank which is partially covered with a vapor-tight seal where the cover is attached to the tank and which cover extends into the liquid below the working level of the liquid to provide a confined area above the liquid and under the cover, which confined area is vented to atmospheric pressure through an opening to which is attached a vapor scrubber and which vapor scrubber contains an absorbent for the volatile liquid.

5. An apparatus for etching a metallic workpiece in a chemical bath consisting of a tank which is partially covered with a vapor-tight seal where the cover is attached to the tank and which cover extends into the liquid below the working level of the liquid to provide a confined area above the liquid and under the cover, which confined area is vented to atmospheric pressure through an opening to which is attached a fume scrubber which contains an absorbent for the fumes produced by the etching action.

References Cited by the Examiner UNITED STATES PATENTS 1,631,052 5/1927 Oertel 134.11 X 3,023,139 2/1962 Van Ietterode 1565 X JACOB H. STEINBERG, Primary Examiner. 

1. A PROCESS FOR TREATING A WORKPIECE IN A LIQUID MEDIA WHEREIN THE LIQUID IS CONFINED IN A TANK WHICH IS PARTIALLY COVERED AND WHICH COVER IS SUFFICIENTLY EXTENSIVE TO ENCLOSE THE ENTIRE PORTION OF THE TANK IMMEDIATELY ABOVE THE WORKPIECE BY A VAPOR-TIGHT SEAL BETWEEN THE TANK AND THE COVER ON ONE OR MORE SIDES, THE REMAINING SIDES OF THE COVER EXTENDING INTO THE INTEFACE OF THE LIQUID, AND EXHAUSTING THE VAPOR CONFINED UNDER THE COVER THROUGH A COLLECTOR BY ITS OWN MOTIVE POWER. 